Many providers of telecommunications services, such as AT&T, maintain large networks of buried fiber-optic cables. Most buried fiber-optic cables have spices every three to five miles. At each splice location, the individual fibers of a cable segment and the cable sheath are bonded to fibers and sheath, respectively, of another cable segment. A water-resistant metallic enclosure (i.e., a splice case) encloses the splice to protect it from moisture. Each splice case typically lies a distance 5-10 feet underground to protect the splice from possible damage. A filter/voltage arrester, of a type known in the art, shunts lightning, and other unnecessary voltages, from the splice case to ground via a sufficiently high resistance path to protect the fiber-optic cable while minimizing leakage to ground of a locate signal impressed on the cable sheath.
While present day filter/voltage arresters generally provide effective protection from lightning and other unnecessary voltages, a close lightning strike may sufficiently damage the arrester, causing it to provide a direct (low resistance) path from the sheath to ground. Hence, a defective filter/voltage arrester will provide a low resistance path to ground for the locating signal impressed on the fiber-optic cable sheath. As a result, attempting to locate a fiber-optic cable by radio detection using the technique described in our U.S. Pat. No. 5,644,237, issued on Jul. 1, 1997 and assigned to AT&T (herein incorporated by reference), may not prove successful, giving rise to mislocation of the cable.
Present day techniques for locating a defective filter/voltage arrester consume a great deal of time and effort. Locating a defective filter/voltage arrester typically requires excavation of every splice case, necessitating not only a technician, but a backhoe and several contract laborers to perform this task. On average, digging up each splice case and testing each filter/voltage arrester takes 4-5 hours. Invariably most of the filter/voltage arresters are uncovered test defect-free, resulting in an unnecessary expenditure of time and effort.
Thus, there is a need for a technique for detecting a defective filter/voltage arrester that avoids the advantages of the prior art.